Thank you for the e-mail, Sergio
I know that your Blackberry will master reset itself after several (usually 10) incorrect attempts to unlock it. To avoid this, I'd rather have you backup your data, and be able to reload software before you re-boot the phone. These instructions can be found at http://support.t-mobile.com/docs/DOC-2072 feel free to send me a private message if this doesn't resolve your issue.
If the BlackBerry is password protected, the user will need to unlock the device first AND enter the password on the computer when prompted before the BlackBerry will allow the computer to connect and before Desktop Manager will allow a backup to be peformed. So, if user does not know password he cannot do a backup.